The wind turbines of a wind park can be operated at a reduced power set-point to ensure a satisfactory balance between the power being delivered by the wind turbines to the electricity network and the power being consumed in the electricity network. The reduced power set-point avoids a situation in which the wind turbines would collectively generate more power than is consumed in the electricity network or grid, which would result in an undesirable increase in frequency of the generated power. Such a reduced power set-point may be stipulated in a grid code. However, wind turbine revenue is generally based on the power that could be delivered by the wind turbine to the grid, i.e. the “available power” of that wind turbine, i.e. the wind turbine revenue may not necessarily be based on the power that is in fact delivered by the wind turbine to the grid. The available power is the power that could be generated by the wind turbine under the prevailing conditions. The most important of these is the current wind speed, since this governs the rotational velocity of the wind turbine's rotor.
Usually, a wind park or even a wind turbine is equipped with one or more wind speed measuring devices such as an anemometer. The measured wind speed is used as the basis from which the available power is estimated. Usually, this is done by consulting a power curve table previously generated in a calibration procedure for that wind turbine type. However, the estimation of available power may be quite imprecise, since it is difficult to measure wind speed over the rotor plane with any degree of accuracy. Wind gusts and turbulence (particularly in the case of a wind turbine that is downstream from another wind turbine) result in poor quality wind speed measurements. Furthermore, even if an anemometer is located directly on a wind turbine, for example on its nacelle, it may not be able to provide an exact measurement for the wind speed at that turbine. For example, if the anemometer is located downwind of the rotor plane, its measured wind speed will be different from the wind speed in the rotor plane, but it is the wind speed over the entire rotor plane that is relevant regarding the amount of power available in the wind.
In another approach, instead of measuring the wind speed using a device such as an anemometer and using the wind speed to determine the available power, the power being generated by the wind turbine can be used to deduce the actual wind speed. From this, the available power can be estimated. However, such an adjustment procedure is complex, and takes some time to be carried out. Furthermore, since this approach requires manual intervention and because many factors must be considered, it is relatively easy for errors to accumulate, resulting in a sub-optimal control of the wind turbine.
Another problem can arise when the control of a wind turbine is adjusted to reduce the level of noise, particularly the aerodynamic noise caused by the rotor blades. If the rotational velocity is reduced on the basis of an incorrect estimated wind speed value, the wind turbine may be operated at a low level of efficiency as a result.